Distance measuring apparatus



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ISTANCE MEASURING APPARATUS Filed March 29, m43

l f7 0 ift/x D Fi@ i Patented .lune i?, i947 y2,4223@ DISTANCE MEASURENG APPARATUS tion of Delaware Applicationgltiarch 29, 19%, Serial No. 481,027

to a'.superregenerative radio apparatus for the measurement of distances.

It is well known that by measuring the time elapsing from the transmission of a radio wave to the reception of the wave at the transmitter position, after the Wave is reflected by striking anobject, a measurement of distance may be obtained from the transmitter to the object. This results from the fact that the speed of radio transmission is substantially constant at 300,000,- 000 meters per second. The present invention measures this time interval in a novel manner with a novel superregenerative circuit.

A superregenerative circuit is an oscillating circuit which is periodically interrupted by quenching the oscillations. The oscillations may be quenched in several ways, such as by driving the plate negative, or driving the cathode positive, or by driving the control grid negative to cut-off'. The quenching may be performed by a. separate voltage generator Whose alternating output. is impressed upon the plate, cathode or grid. The quenching may be also performed by a self -quench action wherein the oscillator tube or tubes are connected in a grid leali circuit with a high grid leali impedance so that the control grid collects more eiectrons than it can dissipate after a few oscillations, driving the grid negative to cut-oi".

The frequency of oscillation at each period of operation is usually determined by a tuned circuit of inductance and capacitance. When the oscillations are quenched and the circuit returned to a condition wherein oscillations may again occur, the chance eifects of thermal agitation, shot effect, etc., start the oscillations and they continue until they are quenched. These oscillations give rise to cathode, plate and grid direct currents, the size of which are directly dependent upon 'the duration of the oscillations before quench. If this superregenerative circuit is used as a receiver, an antenna is coupled to the oscillatory circuit. Ii a carrier wave is received having a frequency close to that of the tuned circuit, voltages will be induced in the circuit and will initiate the oscillations of the circuit when it is returnedto an operable condition after quenching.v

The effect-f a received signal is to start the oscillations at an earlier instant during the operable period of the circuit than is the case when the chance factors of thermal agitation and shot (Cl. 250-L66) eiect start the oscillations. `The result is a group of oscillations of longer duration than in the absence of a signal, resulting in a changed grid, plate or cathode direct current according to the circuit arrangement. Thus a received signal, even though a continuous wave type, is indicated by a denite change in the direct current oi the grid, plate or cathode of the oscillatory tube.

' A second effect of a received signal is to eliminate the characteristic noise or hiss of the usual superregenerative circuit which is present when head-phones are coupled to the circuit. The characteristic noise is caused because of the irregular start of oscillations when the circuit is placed in an oscillating condition. These random oscillations give rise to irregular audio euvelopes, resulting in an audible noise. The e'ect of a received signal is to start the oscillations at a fairly regular time with respect to the oscillatory periods. Since all oscillations are at regular intervals and at a super-audio rate, there is no audio envelope formed (unless the received wave was audio modulated) and the characteristic noise disappears. Thus the disappearance of the characteristic noise is an alternative means of determining the presence of a received signal in the present invention.

As just described, the superregenerative receiver is by nature an oscillatory circuit. The same antenna which induces voltages in the tuned circuit because ofreceived signals, will, by its coupling, also transmit any oscillations in the circuit. Thus a superregenerative receiver with a tightly coupled antenna is also a transmitter, transmitting and receiving simultaneously. The present invention employs this construction to provide a distance measuring device.

The superregenerative circuit of the invention differs from the usual type of quench control in that the quench wave is of the pulse type. The present quench voltage is more accurately referred to as a pulse operating voltage, since the circuit vis in a non-oscillating condition most of the time and oscillates only during a pulse of the separate quench Voltage. The pulse type wave is one wherein the energy of the Wave occurs in a very short time compared to the frequency of the wave. Present type pulse generators are suitable wherein the pulse duration may be one tenth of the frequency. For this reason the quench wave will be referred to as the operating pulse. The result of pulse operation is to transmit and receive radio energy over short periods with long non-operating periods intervening, aiding the precise synchronism of reflected signals with the oscillatory periods of the circuit. Pulse type operation is not essential to the invention, particularly at the higher frequencies, but is advantageous at the lower quench" frequencies.

Distance measuring devices as previously known have insensitive detection circuits compared to a super-regenerative circuit, because the prior devices generally employ insensitive control elements such as diodes to prevent overloading. This, in turn, requires a powerful transmitter with many component parts to allow for the reduced strength of refiected signals. The present superregenerative measuring circuit, on the other hand; is very sensitive and cannot be affected by overload. This makes possible a transmitter of low power having few and light weight component parts. Furthermore, by using the radiation characteristic of a superregenerative receiver, the transmitter and receiver is combined in one unit, further reducing weight.

Another characteristic of present day distance measuring devices is that separate antennas are used foi-'transmitting and receiving. In the present invention the same antenna is used to transmit and receive signals, thus insuring that the construction having the most directional gain for transmitting also has the most directional gain for receiving and vice-versa. Thus the present invention makes use of a single transmitting and receiving circuit to employ a single trans` mitting and receiving antenna.

it is therefore an object to provide a radio distance measuring device of the reiiected wave type wherein one circuit acts as both a transmitter and receiver.

Another object of the invention is to provide a distance measuring device of the reflected wave type wherein one antenna array simultaneously transmits and receives distance measuring radio energy.

.another object is to provide a distance measuring circuit which simultaneously transmits and receives energy, the sensitivity of the receiver being so great that a low powered transmitter is practical, resulting in a single radio set for the entire function which is small and light weight.

An object of the invention is to provide a simple and compact radio apparatus of the superregenerative type.

Another object of the invention is to provide a simple and compact radio apparatus for the measuring 'of distances.

Still another object vis to provide a superregenerative radio distance measuring device wherein the quench frequency indicates the elapsed time between transmission and reception of the signal.

Another object is to provide a superregenera.- tive distance measuring device wherein varying distances are determined by varying the quench frequency.

Another object is to provide a superregenerative distance measuring device wherein signal response is indicated by measuring the plate current of the superregenerative tube.

Another object is to provide a superregenerative distance 'measuring device wherein the reception of a signal is indicated by means producing characteristic noise, the signal being indicated by the absence of the noise.

Another object is to provide a superregenerative absolute altimeter for airplanes.

Other objects and advantages of the invention will be apparent in the following description and claims.

In the drawings forming a part of this specification:

Figure 1 is a schematic circuit of one embodiment of the invention showing a separately quenched grid leak super-regenerative circuit.

Figure 2 is partial circuit diagram showing a modification of the circuit of Figure 1 for grid bias operation, y

Figure 3 is a. partial circuit schematic showing a modication of Figure 1 for self-quench operation wherein a variable resistor is calibrated for different quench frequencies.

Figure 4 is a diagram of the envelope ofthe oscillations occurring during a pulse, showing a wave transmitted by the oscillations of one pulse and reflected and received during the succeeding pulse; and

Figure 5 is a diagram of the envelope of the oscillations occurring in a pulse, showing the wave transmitted during one pulse being reflected and received by the second succeeding pulse.

Referring to Figure 1, a directional transmitting and receiving dipole antenna I0 is manually moveable by the mechanism H and is connected to a loop i2. Loop I2 is magnetically coupled to rods I4 and I6, which form a capacity-inductance tuned circuit for ultra-high frequencies. The tuning of frequency of rods i4 and I6 is varied by mechanically sliding a contactor element it lengthwise of these bars. Contactar i8 is connected to radio frequency choke 20, having a radio frequency ground through condenser 22. The lead from contactar i8 also passes through a direct circuit meter 24, having a zero point for average direct current ows and capable of reading currents which are greater or less than this average direct current' ow, and which are designated as positive and negative respectively. The meter 2d is connected to a winding 2i having a icy-pass condenser 23 connected across it; coupled to winding 2i is a winding 25 to which is connected a pair of headphones 2l. Winding 2i is connected to a battery :'26, the other end of which is grounded. Choke 2U and condenser 22 isolate signal frequencies from the meter, so that only direct current ows through meter 2t, resulting in a direct measure of the plate current of the superregenerative circuit, which will now be described.

Rod it is connected to a plate 28 of a vacuum tube 3d, and the other rod i6 is connected through a grid condenser 32 to a grid 34 of tube li. Grid 35i is connected to ground through a grid resistor 36, for grid leak operation of the tube 3l). A cathode 38 is connected to a winding slt, which is connected to ground. Coupled to winding 40 is a winding l2 which delivers the output of a pulse type variable frequency generator 44, shown in block form. The frequency of generator 44 may be varied by manually rotating a disc 46 in a control box 48, mechanically coupled to variable generator 44. A cathode heater circuit 50 having a. battery 52 completes the circuit of Figure 1,

The generator 4'4 is of the pulse type; that is, the wave form generated is such that the energy is delivered in a relatively short period of time compared to the frequency of the generator. This generator may he of any type, such as is well known in the art, and a pulse duration of approximately two millionths of a second, or two micro-seconds, is easily obtained at 60 kilocycles. The pulse will be of correspondingly shorter duration at higher frequencies. Improvements on present generators for use with improved oscillator circuits may result in an even shorter pulse duration to facilitate accurate measurement of short distances.

The operation of the circuit of Figure l is as follows:

'I'he pulse generator Il drives the cathode 38 alternately positive and negative. When the cathode 33 is positive, or at zero voltage with respect to ground, the tube is inoperative and there are no oscillations in the tube 30. When the cathode 33 is driven negative, thermal agitation causes the tube 30 to oscillate at the frequency of the tuned circuit I4 and I6. This circuit is of the feed-back type, the feed-back being effected` The oscillations appearing in tuned .circuit ld.

and I6 are induced in antenna loop l2 and transmitted by antenna ill. Likewise, by the same coupling, signals received by antenna l are induced in tuned circuit I6 and I6, causing the circuit of Figure 1 to act as a receiver as well as a radio transmitter.

'I'he presence of a received signal is indicated in the circuit of Figure l by the direct current meter 2d. This indication occurs because of the Well-known phenomenon in grid leak superregenerative circuits that the plate current decreases in the presence of a signal. Thus, during transmission of the signal the plate current will be a fairly constant value, but when the signal is received the plate current will decrease and the meter 2i will show a decreased amount of current flowing from the B battery 2B., The presence of asignal is also indicated 'by the lack of a characteristic noise in the phones 2l.

Figure 2 shows the tube 33 of Figure 1 operated as a grid bias tube, wherein the resistor 35 of Figure 1 isfireplaced by battery 31, main-- taining a fairly constant bias voltage of grid 34. As is also well known in the superregenerative art, the plate current increases in the presence of a signal for a tube havingxed grid bias. Thus, the meter 2li of Figure 1 would show an increased current over the normal value when the circuit of Figure lis connected, as shown in Figure 2.

Figure 3 shows a second modiiication of the circuit of Figure 1, showing the tube 30 operated as a self-quenching superregenerative tube instead ofiemploying the separate quench oscillator llt, as shown in Figure l. The grid resistor, 36h is of the variable type, and may be varied as indicated on a calibrated scale 35i to give variable quench frequency. Self-quenching is accomplished by making the grid resistor of high enough impedance in combination with the grid condenser 32h so that a definite time interval is established in which to discharge the grid condenser 32h, according to the value of resistor 36h. When the grid resistor 36h is of high enough impedance the grid 34h collects electrons faster than the resistor will dissipate them, driving to cut-0E, thus quenching the oscillator.

The ,operation of the circuit of Figure 1, and also the circuits of Figures 2 and 3, will now be described with relation to their distance measuring function. Shown in Figure 4 is the envelope of the ultra-high frequencies when a pulse type operating wave is used which is preferable in this distance measuring application, although any wave form could be used with good results. It will be noted that the duration of the pulse is relativelyshort compared to the frequency of the pulse operating voltage. Also indicated in Figure 4 are the ultra-high frequencies which are radiated at each peak of the pulse voltage, the envelope of which is designated as 82. The ultra-high frequencies or circuit il and I6 are transmitted through antenna I0, as indicated by the lines 63, 64 and 65 of Figure 4. If the waves 64 strike an object B, for example an object which may be deliberately sought after by directing the antenna I0 at the object, they will be renected back to antenna l0 and received as an incoming signal, designated by the same number 6I in Figure 4. The effect of an incoming signal is to initiate the high-frequency oscillations 62 at an earlier stage than is normally the case in the absence of a signal wherein oscillations occur by the chance elects of thermal agitation, shot eiect, etc. This increase of oscillations is indicated in Figure 4 by the shaded area of ultra-high frequency oscillations on the second envelope of Figure 4k The angle of reflection in practice is zero degrees but an appreciable angle of reflection is shown in Figure 4 to indicate the passage of time between transmission and reception.

It will be apparent upon an inspection of Figure 4 that a transmitted signal will be received as an incoming signal only when the incoming signal is received during theinterval of time just preceding one of the oscillatory periods as is well known in the art. At all other times the circuit of Figure l, is inoperative and such reflected signals will not be indicated. This is shown in Figure 4 by the waves 63, wherein signals strike object A and are reflected but not received, because the circuit of Figure 1 is inoperative and hence will not indicate the signal. If waves 65 strike an object C and are reflected and received at the peak of oscillations of the second envelope, they will have no effect since they cannot increase the number of oscillations. 'I'hus the responsive part of the operating pulse is the first part.

As mentioned previously, the eifect of a received signal is to increase the number of ultra-high frequency oscillations at each oscillating period. In a grid leak oscillator tube, this results in a decreased plate current and an increased grid current. The decrease of plate current will be registered by meter 24 of Figure 1, and the pulse generator 44 is varied manually by dial 46 until this decrease is a maximum value, as indicated on meter 24. Also, there is a minimum amount of characteristic noise indicated by the head phones 21. This in turn indicates a complete synchronization of the rst part of the operating pulse with the reflected incoming signal. The distance of the object reflecting the signal may be measured directly by Calibrating the dial 48 directly in distance, using the known relation that a, radio wave travels with the speed of light, or three hundred million meters per second, and bearing in mind that the transmitted wave travels twice the distance to the object before it is received. Thus, with directional antennas, la particular object may be selected, the wave trans' mitted, and the pulse generator Varied until theV l received signal response is a maximum. and the distance is then indicated directly on dial 46.

When the circuit; of Figure i is operated as a grid bias oscillator the signal response will be indicated by an increase in plate current which will be registered by meter 2d as an increase over the average plate current. When the circuit of Figure l is operated as a self-quench oscillator, as shown in Figure 3, the calibration of distance is read directly off of scale 39, since variable resistor controls the frequency of the selfquench.

Shown in Figure 5 is a means of increasing the distance of response of the circuit of Figure 1. When the dial 36 is moved to the upper limit of frequency of generator M, it may be rotated further to return the generator M to a lower frequency, but to read the distances on dial t on a different scale. 'Ihe purpose of this is to receive transmitted signals on a second or third pulse succeeding the transmitted pulse, rather than on the pulse directly succeeding the transmitted pulse. This is shown in Figure 5, wherein the transmitted Wave is received by the second succeeding operating frequency pulse, extending the range of operation of the circuit of Figure 1 for the greater distances. Any signal which is received by the second succeeding pulse will be comparatively Weak because of the great distance traveled. Thus a small maximum deflection will indicate that the reflected wave is being received on the second pulse. This feature of the invention is very important, since it extends the operation of a circuit with a pulse type generator of limited top frequency.

From the foregoing description of the invention it is apparent that a superregenerative circuit acting simultaneously as a transmitter and receiver can be used to measure distances; when the antenna l0 is made directional in form it may be used as an altimeter or a directional detection apparatus. The pulse frequency control may be calibrated to indicate distances. Further, automatic frequency changing devices may be used to give a continuous automatic reading. This is preferably done by an automatic sweeping of the frequency of the pulse operating voltage, Then, by interpolating and/or comparing plate current change resulting from the return wave, several means or methods may be used to obtain the automatic type of distance indication. The range of measurement is dependent only on the power, the reecting qualities of the transmitted wave, and the sensitivity of the receiver for the greater distances. In this connection it should be noted that a superregenerative receiver is extremely sensitive. The lower limit of distance measurement is the pulse frequency relative to build up time. For example a quench frequency of one megacycle can measure the distance to an object 150 meters distant, which is a suitable distance for absolute altimeters.

Although the invention has been described with relation to a particular embodiment thereof, it is not limited to this embodiment, nor otherwise except by the terms of the following claims.

I claim:

1. A superregenerative distance measuring device comprising an oscillatory circuit, an antenna coupled thereto, a separate pulse generator variable in frequency, for placing the circuit in an oscillatory condition for a short period compared to the frequency of the pulse generator, and means to indicate the reception of a signal during a pulse, the reception of signal during a pulse of a given frequency being the measure of the distance from a reflecting object.

2. A superregenerative distance measuring device comprising an oscillatory circuit, an antenna coupled thereto, a separate pulse frequency generator for placing the circuit vin an oscillatory condition for a short period compared to the frequency of the pulse generator, and means to indicate the reception of a signal during a pulse, the reception of a signal during a pulse of a given frequency being the measure of the distance from a reecting object,

3. A radio energy distance measuring device comprising a superregenerative circuit for simultaneous transmission and reception, a directional antenna tightly coupled to said circuit so that the energy in the circuit is always transmitted and so that received signals will be impressed upon the circuit, a separate variable quench frequency generator coupled to said circuit, and means to indicate reception of a signal, said generator being varied in frequency so that energy transmitted during one oscillatory period will be received by a succeeding oscillatory period.

4. A superregenerative distance measuring device comprising a self-quenching oscillator circuit having a variable component part to vary the frequency of the self-quench, an antenna coupled with said circuit, said circuit and said antenna both transmitting and receiving during the oscillatory period of said oscillator, said variable component part being varied until the energy transmitted during one oscillatory period strikes an object and is reflected and received during a, succeeding oscillatory period, and means to indicate the reception of a signal.

5. A superregenerative measuring apparatus comprising a grid leak oscillator circuit, an antenna coupled thereto, a variable frequency voltage generator coupled to said circuit to render the circuit periodically operable, at which time the circuit and antenna both transmit and receive radio energy simultaneously, the generator being varied in frequency until the energy transmitted during one period is reflected and received during a succeeding period after striking and being reected by an object, and means to indicate the reception of a signal during a period.

6. A superregenerative measuring apparatus comprising a grid bias oscillator circuit, an antenna coupled thereto, a variable frequency voltage generator coupled to said circuit to render the circuit periodically operable, at which time the circuit and antenna both transmit and receive radio energy simultaneously, the generator being varied in frequency until the energy transmitted during one period is reflected and received during a succeeding period after striking and being reflected by an object, and means to indicate the reception of a signal during a period.

7. A superregenerative measuring apparatus l comprising an oscillator circuit, an antenna coupled thereto, a variable frequency voltage generator coupled to said circuit to render the circuit periodically operable, at which time the circuit and antenna both transmit and receive radio energy simultaneously, the generator being varied in frequency until the energy transmitted during one period is reflected and received during a succeeding period after striking and being reflected by an object, and means to indicate the reception of a signal during a period.

8. A superregenerative measuring apparatus comprising an oscillator circuit, a movable directional antenna coupled thereto, variable means making said circuit periodically operable at which time the circuit and antenna will both transmit and receive simultaneously, the means being varied in frequency until the energy transmitted during one period strikes an object which may be sought out by the directional antenna. and is reflected and received, by a succeeding period, and means to indicate the reception of a signal during a period.

9. A superregenerative measuring apparatus l tionship,means for supplying electric energy to Comprising an oscillatory circuit, an antenna cousaid discharge device, means for periodically varypled therewith, a variable means making said ing the gain in said device at an adjustable rate, circuit periodically operable, at which time the the maximum gain having a value producing oscircuit and antenna will both transmit and recillations in the absence of external stimuli and ceive simultaneously the means being varied in la the minimum gain permitting oscillations to die frequency until the energy transmitted during away, indicating means responsive to changes in one period is reflected and received during a sucthe amount of electric energy supplied to said eeediris pulse, and means 110 indicate the reeepdischarge device, and means for indicating the tion of a signal during a, period. repetition rate of said variations in gain.

10. Distance measuring radio apparatus com- 14. The method of operating a superregeneraprising a. circuit and antenna coupled therewith tive circuit and antenna to measure the distance to simultaneously transmit and receive radio of an object from the antenna comprising, the energy, variable means to render said circuit steps of transmitting oscillation groups at a periodically Operable, and means to indicate the quench frequency, varying said quench frequency reeeptien 0f a Signal, the Variable means being 25 to place the circuit in a receiving condition at the varied until the energy transmitted at one strikes time the reflected energy is intercepted by the an object and is reflected and received on a sucantenna, and utilizing the value of said quench ceedins period, the frequency of the variable frequency to determine the distance of said obmeans giving a measure of the distance to the ject from said antenna. reilecting object. 15. The method of operating a superregenera- 11. In distance measuring apparatus, en antive circuit to measure distances from the circuit tenne. system, an electric discharge device having to an object'comprising the steps of transmitting input and Output Cil'GultS loperatively enneeifed oscillation groups at a quench frequency, varying with said antenna system, said output and input the quench frequency to place the circuit in s. circuits being linked in positive feedback relareceiving condition for reflected oscillation groups tienship, means fOr Supplying electric energy to delayed by periods which are substantially insaid discharge device, means for periodically varytegral multiples of the quench frequency period, ing the gain in said device at an adjustable rate, and utilizing the value of said quench frequency the maximum gain having a value producing osto determine the distance of said object from said cillations in the absence of external stimuli, 40 antenna. means for indicating the amount of electric energy HENRY T. WINCHEL. supplied to said dscharge device, and means for indicating the repetition rate of said variations in REFERENCES CITED gain.

12. In distance measuring apparatus an am m'lef lllcllllgugirferences are of record in `the tenna system, an electric discharge device having input and output circuits operatively connected UNITED STATES PATENTS with said antenna system, said output and input eircuits being linked m positive 4feedback -reis- Number Name Date tionshlp, means for supplying electric energy to 2,211,091 Braden Aug 13 1940 said discharge devicehmeians for periodically vary- 1,92%1'74 Wolf Aug- 29' 1933 ing the gamin said ev ce at an adjustable rate, TENTS the maximum gain having a value producing os- FOREIGN PA cillations in the absence of external stimuli and Number Country Date the minimum gain permitting oscillations to die 108,875 Australia Oct. 20, 1939 Disclaimer nasse-Henry 1 Windel, North Hollywood, Calif.

Patent dated June 17, 1947. Disclaimer filed July l1, 1949,

Bendix Aviation Corporation.

APPARATUS, by the assignee,

away, means for indicating the amount of electric energy supplied to said discharge device,1and means for indicating the repetition rate of said variations ingain.

13.1In distance measuring apparatus, an an.- tenna system, an electric discharge device having input and output circuits operatively connected with said antenna system, said output and input circuitsvbeing linked in positive feedback rela- Drs'rANcn MEAsUnrNs Hereby enters this disclaimer to claims 9, l0, 13, 14, and l5 in said specification.

[O cwl Gazette August 16, 1 9.149.] 

